1. Field of the Invention
The present invention relates to a magnetic recording medium, in which a magnetic recording layer primarily composed of magnetic powder and binder is formed on a non-magnetizable support, and particularly to binder of the magnetic recording layer.
2. Description of the Prior Art
The magnetic recording medium generally comprises a magnetic layer primarily composed of magnetic powder and binder formed on a non-magnetizable support such as a polyethylene terephthalate film. In the prior art, the binder is formed by combining various thermoplastic and thermosetting resins. Further, to improve the mechanical strength of coated layer, various hardening agents such as polyisocyanate compounds are used together with these resins so that a three-dimensional cross-linked structure may be formed by thermosetting. However, such thermosetting method has demerits, such as an insufficientmechanical strength of coated layer, a difficulty in controlling the degree of hardening, and a shorter pot life of the magnetic paint prepared.
A method that hardens the magnetic layer under irradiation has recently been noticed. For example, as disclosed in the Japanese Patent Publication No. 28649/1972, a method is known wherein to improve the wearproof performance of coated magnetic layer and reduce voids thereof a magnetic paint that uses binder formed by mixing an allyl monomer and liquid thermoplastic high molecular prepolymer is coated on a base and then irradiated for polymerization and hardening of these monomer and prepolymer. However, it is noted that in this method the above objects can be achieved only under heavy irradiation since the allyl compound is less reactive. Therefore, as far as an irradiation system of limited dosage capacity is used, the film coating speed is necessarily delayed, which is unfavorable for industrial application. Further, it is still necessary to improve the performance of coated magnetic layer in durability.